Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/21/19
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
920 PM EST Fri Dec 20 2019
High pressure will remain over the East Coast through Saturday. A
low pressure system will then develop over the Gulf of Mexico on
Saturday and could bring precipitation to the forecast area on
Sunday through Monday. Dry and warm high pressure builds in behind
the departing low for the middle of next week.
.NEAR TERM /THROUGH SATURDAY/...
As of 915 PM: Water vapor imagery and RAP 500 mb height fields show
a closed upper-level low center moving east over the TX/OK border
late this evening. Abundant mid and high-level moisture continues to
spill east of this feature over the downstream ridge and across the
southeastern U.S. High clouds will continue to thicken and lower
across the region overnight, although the clouds may be briefly thin
enough from time to time to permit temperatures to radiate down a
bit cooler than previously forecast, and a modest downward
adjustment has been made in a few locations. Otherwise, the
combination of increasing higher clouds and moderating thicknesses
will permit minimum temperatures to remain some two or more
categories above Friday morning values.
The ridge axis will move offshore tomorrow morning as the upstream
H5 low gets cut off from the northern stream. By the end of the
period late Saturday, the upper low is expected to be centered over
the ArkLaTex area as upper-lvl divergence increases over our fcst
area. At the sfc, the center of broad high pressure will continue to
shift to the NE but remain in a proximity to support an incipient
weak wedge by Saturday evening. By this time, a low will develop
over the Northern Gulf of Mexico and begin to move towards our area.
The models have been slowing the development of this system over the
past few runs, and currently they suggest that the deeper moisture
associated with the low won`t begin moving into our southern zones
until Sat. night. As such, PoPs were limited to only slight chance
over our southernmost zones towards the end of the period. For
Saturday, high temps are expected to remain slightly below
climatology as more cloud cover and weak wedging remain in place.
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As of 111 PM EST Friday: The models remain in relatively good
agreement with the track and evolution of a closed upper low,
expected to track over the ArkLaTex region Saturday night and then
along the nrn Gulf Coast region Sunday through Monday. Fortunately,
there is no phasing with the nrn stream, which keeps a broad upper
ridge in place over the Great Lakes and Midwest, thus we are cut off
from any cold air source. So, apart from a very minor concern over
the nrn mountains at onset Saturday night, the passage of this low
should be all rain. How much is the main fcst problem, but first a
brief note about the onset. The model guidance continues to delay
the nwd movement/spread of the light precip well ahead of the low
on Saturday night, to the point where the guidance now suggests
nearly the entire region with perhaps the exception of northeast
GA would remain dry through daybreak Sunday. The new fcst package
will blend in the slower guidance, such that our p-type trouble
zone would only have a slight chance of precip before temps warm
enough above freezing to no longer worry. If anything, the trend
suggests we can sidestep the whole issue. Precip chances should
gradually increase from the south on Sunday as the low reaches the
Gulf Coast, but the northward push will be fighting the dry air
in high pressure over the central Appalachians and Mid-Atlantic
region. Again, precip prob was trimmed back based on the new
guidance. Eventually, however, this should all be overcome late
Sunday and Sunday night as the best mid/upper forcing comes into
play. For now, though, we keep the wrn Carolinas in a precip prob
gradient, with the categorical across the south, likely in the
middle, and still only a chance n of I-40. The low should pass
by to our south on Monday, and so precip prob starts to tail
off, still favoring the srn/ern zones. The best potential for
heavy rain should be across the srn-most part of the fcst area,
especially the Lakelands, but I am wary of the QPF. This looks
something like a situation where we end up with less rainfall than
expected. The passage of the upper system to our south will result
in a stronger-than-normal easterly flow off the Atlantic, but much
of that moisture might be intercepted by convective elements that
form in the stronger isentropic upglide over the coastal plain and
coastal front. The upshot is that by my estimation, if anything
our QPF is more likely to be overdone than underdone. It would
be too early to contemplate any Watches at any rate. Temps will
be slightly below normal Saturday as precip develops, but above
normal on Monday. The upper system moves away Monday night and the
precip should end from southwest to northeast by daybreak Tuesday.
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 205 PM EST Friday: The medium range forecast looks
exceedingly quiet for late December. In the wake of our upper
low, an upper ridge will build in from the west for Tuesday and
will flatten for the middle part of the week. Dry high pressure
will be the rule for the Christmas holiday and again on Thursday,
with temps running well above normal. By Friday, the pattern may
begin to amplify as another upper trof comes eastward out over
the Plains. The only issue will be if moisture can return fast
enough to result in the development of some upslope showers by
the end of the day. The ECMWF is slower than the GFS, and dry,
so for now we keep the precip chances below 10 pct.
.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: High clouds will continue to thicken and
lower through the terminal forecast period. Anticipate cigs AOA 20
kft early, dropping closer to 10-12 kft by tomorrow night. Winds
will remain very light, but gradually acquire more of an ENE to NE
flow component through the period. The main exception will be more
SE to S flow at KAVL through Saturday. All terminal locations should
remain dry through the period, with perhaps just spotty light rain
or showers beginning to encroach from the south on the Savannah
River Valley areas by 00Z Sunday.
Outlook: a Gulf storm system is expected to bring widespread rain to
the region perhaps as early as Saturday night, but more likely
Sunday into Monday, with associated restrictions possible. Dry
conditions should return by Tuesday and persist through the middle
of next week.
02-08Z 08-14Z 14-20Z 20-00Z
KCLT High 100% High 100% High 100% High 100%
KGSP High 100% High 100% High 100% High 100%
KAVL High 100% High 100% High 100% High 100%
KHKY High 100% High 100% High 100% High 100%
KGMU High 100% High 100% High 100% High 100%
KAND High 100% High 100% High 100% High 100%
The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:
Area Forecast Discussion...UPDATED
National Weather Service Hanford CA
354 PM PST Fri Dec 20 2019
Updated Air Quality Issues section
.SYNOPSIS...Dry weather and mild afternoon temperatures
can be expected over the district into Saturday. A storm system
will bring rain and high elevation snow to the region from Sunday
morning into Monday afternoon along with cooler temperatures.
A weak, but colder system will impact the region toward Christmas
eve. An active pattern remains into next week.
Ridge remains in place across the desert southwest which has given
us another nice, dry day across the Central California interior.
High temperatures will end up in the low to mid 60s in the
valley, which is 4 to 8 degrees above average. The ridge will
continue to shift toward the east on Saturday and another warm day
is expected across the area ahead of approaching system. Very
strong southeasterly winds will begin to develop on Saturday
morning in the Fort Tejon and Tehachapi area and continue into
Sunday afternoon. Latest high-resolution HRRR and NAMNEST are
producing very strong winds, with localized gusts up to 65 mph,
especially in the Grapevine area. For this reason, a High Wind
Watch has been issued for the Fort Tejon and Tehachapi zones
beginning Saturday morning through Sunday morning. Gusty winds
are also possible in the West Side Hills on Saturday and Sunday,
and a wind advisory might be needed for this area. Temperatures
on Saturday will be a few degrees warmer than today, with
afternoon highs getting into the mid to upper 60s in the valley.
The upper level trough and associated front moves into the region
on Sunday. Model guidance has been in better agreement on the
timing of the start and end of the heaviest precipitation. Of
note, RFC precipitation guidance has slightly increased
precipitation amounts, and subsequent snowfall totals in the
Sierra have also increased. A Winter Weather Advisory has been
issued for elevations above 4500 feet in the Central Sierra,
including Yosemite, Sequoia, and Kings Canyon National Parks from
7 AM PST Sunday until 10 AM PST Monday. General snowfall amounts
will range between 5 to 10 inches, with locally heavier amounts.
Precipitation within the valley will begin in the early Sunday
morning in Merced and Mariposa counties before spreading southward
toward Kern County by the afternoon.
For precipitation totals from Sunday into Monday morning, between
1/4 and 1/2 of an inch is possible in eastern Merced, Madera, and
Fresno Counties while up to 2/3 of an inch is possible in the
Madera and Mariposa foothills. Due to our rain shadow, all other
areas in the valley will generally be 1/4 of an inch or less,
especially into Kings and Kern Counties. With a more favored
orographics in the Fort Tejon area, up to 1/2 of an inch of
precipitation is possible, and snow levels will remain generally
above 5500 feet. Finally, desert locations can expect between 1/10
of an inch in the Indian Wells valley to 1/4 of an inch elsewhere.
On Monday into Tuesday, near-term models continue to dig a deep
upper level trough into the Southern California/Baja area, with
the corresponding surface low forming off the Southern California
coast by Monday morning. Precipitation is expected to move inland
late Monday into early Tuesday, but the overall confidence in
precipitation amounts is low at this time. What has more
confidence is that as the cold core low moves over the region,
snow levels are expected fall as low as 4000 feet by Tuesday
morning. So, given the busy holiday travel time, possible
impact-based warnings may need to be considered for this Christmas
Going forward from Wednesday onward to the end of the forecast
period next Friday, the pattern remains active with models showing
another system starting to impact the area by late Wednesday.
However past this point, longer-term models are in very little
agreement as the ECWMF digs a deep cutoff low off the CA coast
while the GFS has a more transient upper level pattern.
Strong southeasterly sustained winds of 20 to 30 kts, with local
gusts up to 55 kt are likely in the Tehachapi mountains and valley-
facing side of the Coastal Range starting 12Z Saturday into 18Z
Sunday. Otherwise, VFR conditions will prevail over the central
California interior during the next 24 hours.
.AIR QUALITY ISSUES...
On Saturday, December 21st, 2019, fireplace/wood stove burning
status is: no burning unless registered in Fresno, Kern, Kings, and
Madera Counties. Further information is available at Valleyair.org.
The level of certainty for days 1 and 2 is medium.
The level of certainty for days 3 through 7 is medium.
Certainty levels include low, medium, and high. Please visit
www.weather.gov/hnx/certainty.html for additional information
and/or to provide feedback.
Winter Weather Advisory from 7 AM Sunday to 10 AM PST Monday for
High Wind Watch from late tonight through Sunday afternoon for
Area Forecast Discussion
National Weather Service Jacksonville FL
815 PM EST Fri Dec 20 2019
No major updates made to the forecast this evening. A coastal
trough was lifting northward over the coastal waters, and this has
shifted the bulk of the scattered light showers northward into
southeast Georgia. Isolated showers are possible elsewhere along
the coast overnight. Overnight lows will be in the low to mid 40s
across interior southeast Georgia, the upper 40s to low 50s across
coastal southeast Georgia and interior northeast Florida, and the
mid 50s to around 60 degrees for the northeast Florida beaches.
.PREV DISCUSSION [619 PM EST]...
.Near Term.../through Tonight/...
A trough will be located along the Atlantic coast through Tonight.
This feature will provide for gusty winds, especially at the beach
communities. Lift and convergence associated with the trough will
also provide for a chance for showers, mainly at the coast.
Temperatures will trend above normal.
.Short Term.../Saturday through Tuesday/...
...Potential for heavy rain this weekend...
The region will be between a trough of low pressure along the
Atlantic coast, and an area of low pressure gathering over the
central gulf. Much of Saturday will be dry, with the best chances
for showers near the coast. The warm front associated with the low
is expected to move through late Saturday night through Sunday.
While the models differ in track and timing, the best potential for
heavy rain will be in the overnight Saturday night through Sunday
timeframe. The location of the heaviest rain is still in question,
but a wet period is forecast for the entire forecast area. Gusty
winds will also be expected, especially along the coast.
The low itself is expected to track east across the forecast area
Sunday night through Monday night. A few periods of heavier rain
will be possible with the low passage as well, but there will likely
also be periods of dry weather. Rain chances will decrease from west
to east on Tuesday, as the low pulls further to the east.
Temperatures will trend above normal through Sunday, near normal
Monday, then above normal Tuesday.
.Long Term.../Tuesday night through Friday/...
High pressure will build to the north Tuesday night into Wednesday,
then to the northeast Thursday into Friday. While the chance for
rain will not be zero this period, the chance is too low for
mention at this time. Temperatures will trend above normal this
[Through 00Z Sunday]
MSAS analysis shows decent surface moisture flux convergence along mainly
the Florida coast. Inverted low pressure trough located about 50-60 miles
offshore. KJAX radar depicts bands of shallow low topped showers moving
inland at 25 knots across NE FL. Latest HRRR indicates these showers will
focus on the JAX METRO area and eventually KSSI by 05Z as the rainbands
translate slowly northward tonight. VFR/MVFR with northeast winds 5-10
knots inland, and 10-15 knots with gusts to 20 knots at KSSI and KSGJ.
On Saturday, MVFR at KSSI and KSGJ with northeast winds 15 to 20 knots and
occasional showers moving inland from Atlantic waters, mainly after
18Z. Inland TAF sites VFR with northeast winds 10-15 knots and a few
showers for JAX METRO.
Just beyond the TAF period, IFR conditions develop Saturday Night
as rain associated with a strong low pressure system moves into
the forecast area from the west.
A coastal trough will provide enhanced flow through Saturday. An
area of low pressure will gather over the central gulf during the
weekend. The associated warm front will cross the region Saturday
night through Sunday. The low itself will cross the area Sunday
night through Monday night. Winds and seas will remain elevated
through the weekend into early next week. As the low moves east
Tuesday, high pressure will build to the northwest then north
toward mid week.
Rip Currents: SE GA moderate risk through Saturday
NE FL high risk through Sunday
.PRELIMINARY POINT TEMPS/POPS...
AMG 43 57 49 62 50 / 20 20 80 80 80
SSI 51 60 56 64 53 / 40 30 70 90 90
JAX 53 64 57 68 52 / 50 30 70 80 80
SGJ 57 70 60 70 52 / 20 60 60 80 70
GNV 53 69 59 69 51 / 20 20 60 80 60
OCF 54 73 59 72 52 / 10 20 60 80 60
FL...High Rip Current Risk through Saturday evening for Coastal Duval-
Coastal Flagler-Coastal Nassau-Coastal St. Johns.
AM...Small Craft Advisory until 3 AM EST Tuesday for Coastal waters
from Altamaha Sound to Fernandina Beach FL out 20 NM-
Coastal waters from Fernandina Beach to St. Augustine FL
out 20 NM-Coastal waters from St. Augustine to Flagler
Beach FL out 20 NM-Waters from Altamaha Sound GA to
Fernandina Beach FL from 20 to 60 NM-Waters from Fernandina
Beach to St. Augustine FL from 20 to 60 NM-Waters from St.
Augustine to Flagler Beach FL from 20 to 60 NM.
Area Forecast Discussion
National Weather Service Key West FL
1054 PM EST Fri Dec 20 2019
Our winds have backed away from occasional gale-force gusts over
the waters late this evening, but strong east-northeast breezes
continue thanks to the tight pressure gradient between a stalled
front over the southern Straits and a strong high pressure center
over the U.S. Mid-Atlantic region.
Radar shows a few weak showers or areas of light rain over the
oceanside waters of the Keys this evening. Mesoscale models such
as the HRRR show light rain expanding across the island chain
overnight before retreating and withering away around mid-day
Saturday. In fact, some weak subsidence on Saturday afternoon
will lead to more cloud breaks and temporarily beat back our rain
Beyond Saturday afternoon, we will be watching with interest the
development of a low center over the Central Gulf. It will deepen
and expand as it moves across the northeast Gulf on Saturday night
and Sunday morning. At first, it will bring the stalled boundary
over the southern Straits back north across the Keys as a warm
front around Sunday morning. As warmer and moister low-level air
spreads back north, weak to moderate instability will develop.
Warm fronts commonly come with a strongly veered wind profile and
that will be the case here. Such a wind profile is favorable for
organizing and sustaining convective updrafts, but the lack of
strong instability will be the main limiting factor. The most
likely place to get strong or possibly severe storms on Sat
night/Sunday morning would be our far western Gulf waters near the
On Sunday evening, a cold front trailing from the low center will
enter our western waters, eventually exiting our eastern waters
on Monday morning. This front is likely to be accompanied by a
broken squall line of thunderstorms. Any discrete cells that
develop in advance of the main squall line will find a more
favorable environment of both stronger instability and wind shear
for sustaining updrafts and organizing convection. Convective
wind gusts of 40-45 knots appear to be the main threat at this
time. Will be watching this setup. The SPC Day 3 outlook currently
has the Keys in a marginal risk of severe weather on Sunday and
Have removed the Gale Watch from the remaining waters, since it no
longer looks like there is much possibility to hit a gale-force
wind. Recent wind obs shows the start of a slow decreasing trend
in speeds that should continue through sunrise. Nonetheless,
strong to near-gale NE-E breezes will continue under a tight
pressure gradient between a stalled front over the southern
Straits and strong high pressure centered over the U.S. Mid-
Things will start to change more noticeably on Saturday. Low
pressure will develop over the central Gulf, deepening as it
moves through the northeast Gulf on Saturday night and Sunday
morning. A trailing cold front will cross the Keys waters late
Sunday into early Monday. The cold front will be followed by a
shift to strong west-northwest breezes.
Low pressure will then exit further and further east into the
Atlantic on Tuesday and Wednesday, and high pressure will settle
southward into the Southeast U.S..
Radar shows a few areas of sprinkles or light rain over the
Straits adjacent to the Keys this evening. Several pieces of
model guidance suggest a temporary expansion of the light rain
across the island terminals late tonight and Saturday morning, or
from about 10z-16z. On Saturday afternoon, model time-height
sections show a modest increase in subsidence, which should help
to scatter and thin out some of the lower cloud layers. Have
therefore shown some improvement in sky cover on Saturday
GM...Small Craft Advisory for GMZ031>035-042>044-052>055-072>075.
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Area Forecast Discussion
National Weather Service Norman OK
541 PM CST Fri Dec 20 2019
00Z TAF discussion.
MVFR ceilings will overspread most sites quickly over the first
couple of hours of the forecast. The exceptions will be CSM/WWR
which should remain VFR. Could see some IFR conditions develop
late tonight in central Oklahoma along with some potential for
drizzle. MVFR ceilings may linger through much of the day Saturday
as well. Winds will remain light.
.PREV DISCUSSION... /issued 403 PM CST Fri Dec 20 2019/
There is a chance for drizzle/light rain over southern/eastern
OK this afternoon into tomorrow morning as the closing low
pressure trough tracks across southern OK overnight. Patchy fog is
also possible early tomorrow morning across western OK and
western north TX, and there is the possibility of more widespread
fog Sunday morning.
Latest water vapor loop (21Z) places the center of the upper low
near Childress, TX with the midlevel dry slot covering the western
two thirds of Oklahoma. Low-level clouds developed over
southern/central portions of the state this morning and are still
present. Forecast soundings from both the RAP and NAM suggest
that light rain might be possible farther north into southern
portions of the OKC metro overnight as well, and have thus bumped
up the POPs slightly for this area. Added drizzle to north OK
tonight, where low level saturation is suggested to be more
shallow. In addition, parts of western north TX and western OK
may see patchy fog early tomorrow morning. More widespread fog
appears possible Sunday morning as multiple sounding sites
indicate light winds and saturation beneath a sharp surface
Sunday into Tuesday, daytime highs will trend upwards into the
60s. Winds are forecast to increase Sunday into Monday and RH
values will drop to 15-20 percent across western Oklahoma - an
enhanced fire weather risk appears possible.
The next cold front is expected on Wednesday and high
temperatures will return to the 50s by Thursday. Models have not
been very consistent with precipitation for middle of next week.
However, precipitation appears more likely toward the end of next
week and into next weekend. For now, not enough evidence to
introduce wintry precip, but will need to watch for changes in
thermal profiles as the event draws closer.
.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK 36 50 33 57 / 10 10 0 0
Hobart OK 30 53 29 59 / 0 10 0 0
Wichita Falls TX 39 50 32 62 / 10 10 0 0
Gage OK 24 54 28 65 / 0 10 0 0
Ponca City OK 32 50 30 57 / 0 0 0 0
Durant OK 39 48 34 57 / 40 30 0 0